Conventionally, a HUD device is known, which is mounted in a mobile unit to display a virtual image of an imagery to be recognized by an occupant by projecting the imagery on a projection component in the mobile unit. A HUD device described in Patent Literature 1 includes a projector which projects an imagery, and an expansion lens as an expansion optical system which expands and projects the imagery from the projector to a projection component. In Patent Literature 1, a control part estimates a relative position of the sun relative to a vehicle based on positional information.
In Patent Literature 1, a light reflected on the plane where the sunlight passes the expansion lens is estimated based on the information, and it is determined whether a reflection angle of the reflected light is within a preset angle range. The expansion lens is rotated based on the determination result, such that the expanded image can be recognized with high visibility without noise caused by the reflected light.